Method and apparatus for browning exterior surfaces of foodstuff in an electronic range

ABSTRACT

Browning the outer external surface of a foodstuff with infrared rays emitted from an infrared source at the same time the interior of the foodstuff is processed in an electronic range. The foodstuff and the source for emitting the infrared rays are placed in a region where electromagnetic waves are radiated from a high frequency generator. The infrared source is constructed by evaporating a conductive thin film on the outer surface of a dish or other vessel for holding the foodstuff. Alternately, crystallized glass having fine pieces of carbon fibres scattered throughout may form the infrared source. In yet another embodiment, a layer of silicon carbide may be formed on an insulating base plate. In each of the embodiments, the infrared heat is generated by the action of the electromagnetic waves on the specially constructed source.

Umted States Patent 1 1 r 3,783,220 Tanizaki 1 Jan. 1, 1974 METHOD ANDAPPARATUS FOR 2.730.598 l/1956 Lytle 219/543 BROWNING EXTERIOR SURFACESor S v aun ers et a 1 FOODSTUFF IN AN ELECTRONIC RANGE 3.177.341 4/1965Woody et a1. 219/543 X [75] Inventor: Hiroshi Tanizaki, Kamakura, Japan,364. 65 8/1967 Hurko 219/543 X 3.544.361 12/1970 Servais 117/124 [73]Assignee: Yamamizu Shoji Kabushiki Kaisha,

Tokyo, Japan FOREIGN PATENTS OR APPLICATIONS Filed Jun 1971 1,049,019l/1959 Germany 219/10.55

[21] Appl. No.: 158,287 Primary Examiner-R. F. Staubly AssistantExaminer-Hugh D. Jaeger [30] Foreign Application Priority DataAttorney-Price, Heneveld, Huizenga & Cooper I July 6, 1970 Japan45/58847 [57] ABSTRACT [52] U.S. C1 219/10.55, 99/451, 219/543 Br ng theouter x l surface of a fo tuff [51] Int. Cl. H05b 9/06 ith infr re raymitted from an infrared source at [58] Fi ld f S hm 2]9/1() 55, 543; thesame time the interior of the foodstuff is processed 99/45] in anelectronic range. The foodstuff and the source for emitting the infraredrays are placed in a region [56] References Cit d where electromagneticwaves are radiated from a high frequency generator. The infrared SOUI'CC15 con- 2.830.162 4/1958 Copson et al 219/1055 meted by evaporaimg aconducnve film the 3,320,396 5H967 Boehm u 219M055 outer surface of a(11811 or other vessel for holdmg the 359L751 7/197] GoltSos 219M055foodstuff. Alternately, crystalllzed glass having fine 35397 W970Levinsonm 219M055 pieces of carbon fibres scattered throughout may form3.585.258 6/1971 Levinson 219 10.55 the infrared source. In y n th rembodiment, a 3.662.141 5/1972 Schauer, Jr. 219/10.55 layer of siliconcarbide may be formed on an insulat- .9 89 93 Jone 3 UX ing base plate.In each of the embodiments, the infra- 5 9 6951 Under l r 219/543 redheat is generated by the action of the electromag- 2.546.707 3/1951Mocha 7/54 netic waves on the specially constructed source. 2,566,346/1951 Lytle et a1 117/54 2,614,944 10/1952 Lytle 117/54 10 Claims, 3Drawing Figures METHOD AND APPARATUS FOR BROWNING EXTERIOR SURFACES OFFOODSTUFF IN AN ELECTRONIC RANGE BACKGROUND OF THE INVENTION.

The invention relates to an apparatus and method for browning theexterior surfaces of a foodstuff in an electronic range by providing anadditional infrared heating of the foodstuff as a phenomena of heatingof a dielectric through high frequency.

When a foodstuff is roasted directly with a gas flame or is grilled bythe radiation from a nichrome heater, the heating of the foodstuff goeson slowly from the exterior to the interior of the foodstuff. Theexterior of V the'foodstuff may be done to the extent of scorching whilethe interior may remain in a state of half roasting. For example, aroast may be well done on the exterior while remaining rare in theinterior.

In case of heating a foodstuff by an electronic range, the cause ofheating is due to molecular motion in the interior of the foodstuff whenit is subjected to high frequency electromagnetic radiation. Accordingto the characteristic of high frequency dielectric heating, thefoodstuff itself becomes a heat generating body and the interior andexterior thereof are cooked equally and swiftly.

However, according to the time honored custom, it is a matter ofnecessity from the point of view of taste, of sight and for generalgastronomic appeal to have some browned portion on the outer surface ofan individual serving of the food. In the above electronic range, it isimpossible to obtain such browning of the outer portions as the interiorand the exterior of the food is equally cooked.

OBJECTS OF THE PRESENT INVENTION It is therefor a primary object of thisinvention to provide an apparatus for browning the exterior surface of afoodstuff while preparing same in an electronic range.

Another object of the invention is to provide a method and apparatus forheating the interior of the foodstuff sufficiently in a short time aswell as simultaneously browning the exterior thereof.

Another objectof the invention is to provide an infrared sourcegenerating body for use in an electronic range.

It is yet another object of the invention to provide a means ofmanufacturing a heat generating body for use in an electronic range tobrown the exterior surfaces of foodstuffs processed therein.

The present invention provides an apparatus and method in which a sourcefor emitting infrared radiation and a foodstuff to be heated are put ina region of propagation of electromagnetic waves emitted from a highfrequency generator. The whole of the foodstuff to be heated issubjected to high frequency dielectric heating and at the same time, theexterior surface of the foodstuff is browned by the infrared radiationemitted from the infrared source.

DESCRIPTION OF THE DRAWINGS The details of the present invention will bebetter understood from the following description and with reference tothe accompanying drawings in which:

FIG. 1 diagrammatically illustrates the operation of the presentinvention;

FIG. 2 is a perspective view of an electronic range incorporating thepresent invention;

FIG. 3 is a perspective view illustrating an alternate embodiment of theheat generating source.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, aconventional electronic range is illustrated in somewhat schematic form.A foodstuff l to be processed is placed in the heating chamber 4 of therange and is subjected to high frequency electromagnetic radiation(illustrated by the numeral 6) which is generated by a high frequencygenerator 9 (FIG. 2). The high frequency radiation 6 traverses theinterior 4 of the range and acts upon the foodstuff 1 contained therein.As is well-known to those skilled in the art, molecular motion in theinterior of the foodstuff causes heating and as a result the foodstuffitself becomes the heat-generating body. As mentioned above, foodstuffprepared in this manner is quickly and rapidly cooked and the interiorand exterior surfaces are generally cooked to about the same degree.

In order to brown the outer surfaces of the foodstuff whilesimultaneously subjecting it to the high frequency electromagneticradiation, a conductive thin film 3 may be formed on the surface of adish or other vessel 2 in which the foodstuff is contained when placedin the oven. Altemately, an insulating plate 5 having a similarconductive thin film 3 thereon may be provided at an appropriateposition in the heating chamber 4 of the electronic range.

In operation, an electronic vortex current is generated in the thin film3 by the action of the electromagnetic waves 6 causing the thin film toheat and become an infrared heat source. Accordingly, the infraredradiation from the thin film 3 located on the dish 2 or on theinsulating plate 5 radiates infrared radiation to thereby applyadditional heat to the exterior surfaces of the foodstuff l at the sametime the interior of the foodstuff is heated by the passage of the highfrequency electromagnetic waves therethrough.

As mentioned above, the conductive thin film 3 may be formed on thesurface of the dish 2 or on the insulating plate 5. In the case of adish, it is preferable to provide a material such as glass having a lowcoefficient of expansion and heat resisting properties. A thin tin oxidecoating is glazed at a high temperature to the surfaces of the dishthereby providing a conductive thin film on its surfaces. Altemately, asimilar thin film layer of tin oxide may be provided on an insulatingplate 5 at an appropriate location within the range. If the thickness ofthe layer 3 is about 0.5 p. the approximate resistance of the dish 2 orthe insulating plate 5 will be on the order of 1.5 X l0- 0cm. As acontrast, for example, the resistance value for copper is 1.7 X 10 Gemand, for nichrome, 1.1 X 10 0 cm.

A conductive glass 3 constructed as above exhibits excellent performancewhen utilized as an infrared heat generating source in an electronicrange. This is due to the combined effect of the electrical insulatingproperties of the glass itself and the electrical conducting propertiesof the coated film. If the region of wavelength is in the neighborhoodof the maximum emissivity of infrared radiation is made to lie somewhereat more than 3 p. there is little change in the heating effect as thesurface color of the object varies during cooking. Also, the efficiencyof heat transfer radiation is high.

In the practice of the present invention, by forming a conductive thinfilm 3 on the dish itself no modifications are necessary to the range.The foodstuff is simply placed in the dish and the range is operated ina conventional manner. The coating on the glass may be transparent orattractively colored. The dish may also be utilized as a convenientserving dish.

It may, therefor, be seen that an infrared heat generator is suppliedwithout the necessity of a separate electrical power source within therange. Similarly, the insulating plate may be arranged in the range inany convenient manner so that it may be removed if desired. In eithercase, a separate power source is not required as the thin filmconductive layer 3 provides the infrared heat source as theelectromagnetic waves act upon it.

As is well-known to those skilled in the art, electronic ranges of thetype herein described are instantaneous in their operation. The highfrequency generator may be turned on or off as desired. Consequently,objects contained within the oven will instantly be subjected to veryhigh frequencies and the resultant high temperatures. Conversely, thearticles therein may be subjected to an abrupt cooling. Accordingly,conductive glasses used therein must be able to withstand these extremevariations and yet must effectively transfer the infrared radiation. Thebase of the conductive glass plate may, therefore, be prepared asfollows:

The principal materials (Si O Alggg l iz o, etc.) are added with agentsfor nucleus formation (Zr 0 Ti 0 etc.) and these are mixed completely.The mixture is then fused at a high temperature of about l,600C and,processed by molding it to the required shape and dimension. The moldedshape is then annealed to remove stresses. The raw material at thisstage of process remains amorphous and the finished product is obtainedby giving primary heating (700800C) continuously in an oven forcrystallization to keep the original form of the raw glass. The glass isthen subjected to a secondary heating treatment (800900C).

The above primary and secondary heat treatments are the heating schedulebased on the theory of generation and growth of crystals. At the firststage of the primary heat treatment, small nuclei having dimensions offrom several ten to several hundred of A are generated, then after theelevation of the temperature amorphous regions are formed around thenuclei.

If the secondary heating state is held for 1-5 hours the above amorphousregions change to B-Eucryptite (Li2O.Al2 O 2 SiO;) and M,o and tomicrocrystals of solid solution of SiO Up to this stage of process thecrystalline particles are less than 0.01 -0.5 [.L, of smaller dimensionthan the wavelengths of visible rays and the index of refraction oflight is the same as that of the glass. The transparent products arethereby obtained. If semi-transparent or white objects are desiredfurther heating process may be applied.

The glass obtained by the above process is to be defined as acrystallized glass".

In another embodiment, a conductive glass as shown in FIG. 3 may beprovided. Fine pieces of carbon fibre 11 are sprinkled and adhered to adish formed of electrically insulating and heat-resisting glass, ceramicor the like.

The above carbon fibre I l is a popular name for fibres of cellulose oracryl baked (carbonized) at a temperature exceeding 1,000C on immersingthem in nitrogen or alchol by isolating from oxygen- In yet anotherembodiment, a layer of silicon carbide (SiC) may be formed as the thinfilm 3 on a dish using heat resisting glass or ceramic as the principalbody. Because of its high melting point this embodiment operatessatisfactorily in a high temperature environment.

Reasonable variations and modifications are possible within the scope ofthe foregoing disclosure, the drawings and the appended claims withoutdeparting from the spirit of the invention.

What is claimed is:

1. In an electronic range having a chamber in which a foodstuff issubjected to high frequency electromagnetic radiation for the cookingthereof, the improvement comprising: emitting means in said chamber foremitting infrared radiation in response to said electromagneticradiation, said emitting means including a heat-resistant, electricallynonconductive plate and converting means formed on a surface of saidplate for converting such electromagnetic radiation to infraredradiation, said converting means being an electrically conductive thinfilm, said emitting means acting upon a foodstuff contained in saidchamber to brown the outer surfaces thereof.

2. An electronic range as defined in claim 1 wherein said convertingmeans comprises a thin film of tin oxide formed on said surface of saidplate, said film having a thickness of about 5 microns.

3. An electronic range as defined in claim 1 wherein said convertingmeans comprises: a quantity of carbon fibre fixed on said surface ofsaid plate.

4. An electronic range as defined in claim 1 wherein said convertingmeans comprises: a layer of silicon carbide fixed on said surface ofsaid plate.

5. A method of browning the surface of a foodstuff in an electronicrange having a chamber in which the foodstuff is subjected to highfrequency electromagnetic radiation for the cooking thereof comprising:the steps of providing a container having a thin film of tin oxideformed on at least one surface thereof for emitting infrared radiationin response to electromagnetic radiation in said chamber; placing thefoodstuff in said container in contact with said container; andsubjecting said foodstuff and said container to said high frequencyradiation whereby said foodstuff is cooked by said high frequencyradiation and the outer surface thereof is browned by the infraredradiation converted by said tin oxide film from said high frequencyradiation.

6. The apparatus as defined in claim 2 wherein said plate is acrystalline glass.

7. Apparatus for converting high-frequency electromagnetic energy intoheat energy in an electronic range for browning the outer surface of afoodstuff subjected to such high-frequency radiation for the cookingthereof comprising:

a container for the foodstuff, said container having a heat resistant,electrically insulating base material, and a thin film of tin oxideformed on said base material on at least one surface thereof, saidcontainer adapted to support the foodstuff whereby a foodstuffcontacting said container is browned by said heat energy while theinterior of such foodstuff is cooked by said high-frequencyelectromagnetic radiation.

energy converted by said film resulting solely from said radiation foracting upon a foodstuff contained within said chamber to brown the outersurface thereof.

9. The improvement as set forth in claim 8, wherein said thin film istin oxide.

10. The improvement as set forth in claim 9, wherein said thin film hasa thickness of about 5 microns.

" I fuNmsnsir/"P155 PA'mN'i. O'JPFKIEE (3121i 1 HA HA i IL 01* COREY-LCHON Patent No. 3 3H Dated January 1, 1974 Invemofls) Hiroshi Tanizaki Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 31; v Change "5 microns" to -0.5 microns- Column 6; line7; v 7

Change "5 microns" to 0 .Sv microns- Signed endvsea led this 10th day ofSeptember 1974.

(SEAL) Attest H MCCOY M. GIBSON, J'R'. K I c. MARSHALL DANN AttestingOfficer v Commissioner of Patents CERFH11CAHL' OF CORRECTIQN Patent No.3,733,220 Data; January 1, 1974 Inventor) H1rosh1 Tanlzakl It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 31;

Change "5 microns" to -0.5 microns- Column 6, line 7;,

Change "5 microns" to --0.5 microns-;-.

Signed end sealed this 10th day of September 1974.

(SEAL) Attest! M MCCOY M. GIBSON, JR V C. MARSHALL DANN AttestingOfficer Commissioner of Patents

2. An electronic range as defined in claim 1 wherein said convertingmeans comprises a thin film of tin oxide formed on said surface of saidplate, said film having a thickness of about 5 microns.
 3. An electronicrange as defined in claim 1 wherein said converting means comprises: aquantity of carbon fibre fixed on said surface of said plate.
 4. Anelectronic range as defined in claim 1 wherein said converting meanscomprises: a layer of silicon carbide fixed on said surface of saidplate.
 5. A method of browning the surface of a foodstuff in anelectronic range having a chamber in which the foodstuff is subjected tohigh frequency electromagnetic radiation for the cooking thereofcomprising: the steps of providing a container having a thin film of tinoxide formed on at least one surface thereof for emitting infraredradiation in response to electromagnetic radiation in said chamber;placing the foodstuff in said container in contact with said container;and subjecting said foodstuff and said container to said high frequencyradiation whereby said foodstuff is cooked by said high frequencyradiation and the outer surface thereof is browned by the infraredradiation converted by said tin oxide film from said high frequencyradiation.
 6. The apparatus as defined in claim 2 wherein said plate isa crystalline glass.
 7. Apparatus for converting high-frequencyelectromagnetic energy into heat energy in an electronic range forbrowning the outer surface of a foodstuff subjected to suchhigh-frequency radiation for the cooking thereof comprising: a containerfor the foodstuff, said container having a heat resistant, electricallyinsulating base material, and a thin film of tin oxide formed on saidbase material on at least one surface thereof, said container adapted tosupport the foodstuff whereby a foodstuff contacting said container isbrowned by said heat energy while the interior of such foodstuff iscooked by said high-frequency electromagnetic radiation.
 8. In anelectronic range having a chamber in which a foodstuff is subjected tohigh frequency electromagnetic radiation for the cooking thereof, theimprovement comprising: a heat resistant, electrically non-conductiveplate and an electrically conductive thin film of a material absorptiveof said radiation applied to a surface of the plate for absorbing suchelectromagnetic radiation and converting it into heat energy the energyconverted by said film resulting solely from said radiation for actingupon a foodstuff contained within said chamber to brown the outersurface thereof.
 9. The Improvement as set forth in claim 8, whereinsaid thin film is tin oxide.
 10. The improvement as set forth in claim9, wherein said thin film has a thickness of about 5 microns.